Electronic Properties of Spin Controlled Semiconductor Nanostructures

该小组的成立是为了研究和阐明自旋控制的超导材料和纳米结构的电子结构和传输特性。为此，研究了铁磁半导体及其相关异质结构的生长和加工，这些材料和结构的输运/磁性/光学性质，以及电子结构计算和输运性质理论。研究结果总结如下：1.由半导体材料制成的铁磁/非磁三层结构表现出自旋相关散射、层间耦合和隧穿磁电阻效应。发射极为（Ga，Mn）As的共振隧穿二极管在低于铁磁转变温度时表现出自发电流峰分裂。同时，还研究了铁磁（Ga，Mn）As对GaAs结构的电自旋注入。（H.Ohno等人）2.研究了（In，Mn）As和（Ga，Mn）As的低温磁性和输运性质.我们的一个重要发现是，在较低温度下进行热处理可大大改善晶体质量。软X射线吸收实验表明，这种改善是由于过量As原子的蒸发。（S.Katsumoto等人）3.对Ⅲ-Ⅴ族稀磁半导体（Ga，Mn）As的电子能带结构进行了第一性原理计算。最近邻的3d过渡金属自旋之间的磁相互作用是铁磁性的V，Cr，Mn。（N.Suzuki等人）我们已经制备了具有高度旋转对称性的人工原子/分子。对于人工原子，（i）原子的性质，如壳层填充和遵守洪德规则和（ii）各种自旋态的转变作为磁场的函数已被观察到。对于人工分子，我们已经研究了新的自旋效应，如自旋封锁，同位旋封锁，自旋相关隧穿，等等。

This group was formed to study and elucidate the electronic structure and the transport properties of spin-controlled semiconductoring materials and nanostructures. To this end, the growth and processing of ferromagnetic semiconductors and their related heterostructures, transport/magnetic/optical properties of these materials and structures, and the electronic structure calculation as well as the theory of transport properties were investigated. The summary of the research results is :1. Ferromagnetic/non-magnetic trilayer structures made of semiconductor showed spin-dependent scattering, interlayer coupling and tunneling magnetoresistance. Resonant tunneling diodes with (Ga, Mn) As emitter exhibited spontaneous current peak splitting below the ferromagnetic transition temperature. Also electrical spin-injection from ferromagnetic (Ga, Mn) As into a nonmagnetic GaAs structure was demonstrated. (H.Ohno et al.)2. Magnetism and transport in (In, Mn) As and (Ga, Mn) As at low temperature was studied. One of our important finding is that crystalline quality is much improved by heat treatment at comparatively low temperature. Soft X-ray absorption experiment is making it clear that the improvement is due to the evaporation of excess As atoms. (S.Katsumoto et al.)3. First-principle electronic band-structure calculations are carried on III-V based diluted magnetic semiconductors (Ga, Mn) As. The magnetic interactions between the nearest neighboring 3d transition-metal spins are ferromagnetic for V, Cr, Mn. (N.Suzuki et al.)We have prepared an artificial atom/molecular having a high-degree of rotational symmetry. For artificial atom, (i) atom-like properties such as shell filling and obeisance of Hund's rule and (ii) various transitions of spin states as a function of magnetic field have been observed. For artificial molecules we have investigated novel spin effects such as spin blockade, isospin blockade, spin-dependent tunneling, and so on. (Tarucha et al.)